First you have to determan if its a lower engine sound an upper engine sound---a lower engine sound will not go away-you may hear it less with a fresh oil change or thicker oil but rest asured it doesn't just come and go. When you have the vehicle running at normal operating temp, just give it enough gas to come off idle - you can usually hear the lower end that way. If this is the case-and you can't afford to replace or rebuild, change the oil and use a heavier oil - baby it until it dies. The harder you drive it, the shorter its life span.
An upper end noise is more like a tapping sound which can be caused by a stuck lifter in which case I would put an oil additive in with a fresh oil change--(not an flush but additive like Wynns, Lucas or BG products). You don't want to use a flush because at 145k , if the engine was negelected the proper maintance, you will have deposits caked on oil inside the engine and you don't want that stuff coming loose. Good Luck
